Determination of residual oil in a formation

ABSTRACT

A method for determining the amount of residual oil remaining in an oil bearing formation after primary production which includes the sequential steps of: 
     A. logging the formation to obtain logging data measurements of the relative quantities of residual oil and formation water present in the formation; 
     B. injecting a sufficient amount of an oil miscible solution through the bore hole into the formation to displace substantially all of the residual oil in the formation surrounding the bore hole; 
     C. injecting a sufficient amount of water into the formation through the bore hole to displace substantially all of the oil miscible solution thereby rendering the formation being tested substantially 100 per cent water saturated; and 
     D. logging the formation for a second time to obtain logging data measurements which, when compared with the logging data measurements of the initial log indicate the amount of residual oil present in the formation.Iadd., wherein said logging data measurements are obtained by employing a reservoir property logging apparatus selected from the group consisting of resistivity logging apparatus, sonic logging apparatus and density logging apparatus.Iaddend..

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of logging subterranean reservoirstraversed by well bores, particularly hydrocarbon-containing reservoirs.In one aspect this invention relates to a method for determining theamount of residual oil in an oil bearing formation employing loggingtechniques. In yet another aspect, this invention relates to a methodfor determining the amount of residual oil present in subterraneanreservoirs traversed by well bores wherein such residual oil saturationproperties are detected by the use of a log-reservoir floodinjection-log technique.

2. Brief Description of the Prior Art

The importance of determining residual oil in place by means ofsub-surface logging techniques has been recognized for some time. At thepresent new oil fields are becoming more difficult to discover and moreattention is being given to secondary and tertiary methods for oilrecovery in oil fields. However, prior logging techniques have requiredthe use of radio-active materials or substantial knowledge of thesubterranean formation such as porosity, lateral penetration, make up ofthe formation, and the like, if one is to obtain reliable informationfrom such logging techniques. Therefore, while numerous methods havebeen and are being used to determine the amounts of residual oil presentin reservoir formations, all of the prior art methods, regardless as towhether they employ core analysis, well testing, well logging, and thelike, have certain limitations. Pitfalls and the rather unsatisfactoryaccuracy of the results using these conventional techniques have createda serious problem for the oil industry. Because of the high costs inrecovering such residual oil through secondary or tertiary means, it isdesirable and of utmost importance that an accurate, dependable methodbe developed for determining the amount of residual oil remaining insuch formations. Until the present invention, there was no satisfactorymethod for accurately and inexpensively determining the amount ofresidual oil.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a method fordetermining the amount of residual oil in a subterranean oil bearingformation.

Another object of the invention is to provide a new and improvedtechnique for indicating directly the residual oil concentration in asubterranean formation by the use of reservoir property loggingtechniques.

Still another object of the present invention is to provide an improved,accurate technique for determining the amount of residual oil in asubterranean formation which is not dependent upon reservoir propertiessuch as porosity, composition of said formation, and the like.

Other objects, and advantages of the present invention will becomeapparent to those skilled in the art from a reading of the followingdetailed description.

SUMMARY OF THE INVENTION

According to the present invention we have now discovered an improvedtechnique for determining the amount of residual oil in an oil bearingformation penetrated by a well-bore. More specifically, we have found animproved technique for determining residual oil in place by means ofsub-surface logging techniques.

Specifically, the technique for determining the residual oil in an oilbearing formation which has been penetrated by the borehole of a wellincludes the sequential steps of:

a. logging the formation to obtain logging data measurements of therelative quantities of residual oil and formation waters present in theformation;

b. injecting a sufficient amount of an oil miscible solution through theborehole into the formation to displace substantially all of theresidual oil in the formation surrounding the borehole;

c. injecting a sufficient amount of water into the formation through theborehole to displace substantially all of the oil miscible solutionthereby rendering the formation being tested substantially 100 percentwater saturated; and,

d. logging the formation for a second time to obtain logging datameasurements which, when compared with the logging data measurements ofthe initial log indicates the amount of residual oil present information.Iadd., wherein said logging data measurements are obtained byemploying a reservoir property logging means selected from the groupconsisting of resistivity log means, sonic log means and density logmeans.Iaddend..

In carrying out the logging measurements in the technique of thisinvention, any reservoir property determining log measurement means canbe employed. Further, accurate and reliable measurements can readily beobtained without knowledge of the porosity of the reservoir formation,and in clean and or shaly reservoir rock, each of which can be eitherwater wet or oil wet.

DETAILED DESCRIPTION OF THE INVENTION

As previously stated, the present invention relates to a unique methodfor determining the residual oil present in oil bearing formations whichhave been penetrated by the borehole of a well. Broadly speaking, themethod employs a combination of log-injection-log techniques todetermine the amount of residual oil present in a subterranean oilbearing formation. By employing the method of the present invention forlogging a drill hole to determine the amount of residual oil present inan oil bearing formation, one readily overcomes all the objectionablefeatures of the prior art processes that have been enumerated above.

In determining the amount of residual oil present in an oil bearingformation, we have found that an accurate determination can be obtainedwherein the formation, containing both residual oil and formation water,is logged by reservoir property log means to obtain logging datainformation on the amount of fluids present in said formation. Once thelogging data has been obtained the formation is treated by miscibleflooding techniques to displace substantially all of the residual oil inthe formation surrounding the borehole of the well. The amount ofmiscible solution employed in the reservoir flooding step can varywidely but is in an amount sufficient to remove substantially all of theresidual oil from the formation in the area surrounding the borehole toa distance exceeding the radius of investigation of the logging meansbeing employed to obtain the logging data. After the flooding operationhas been completed a sufficient amount of water is injected into theformation through the borehole of the well to displace substantially allof the oil miscible solution, thus rendering the formation beinginvestigated substantially 100 percent water saturated. A second log isthen made of the formation to obtain logging data measurements, which,when compared with the logging data measurement of the initial log,indicates the amount of residual oil present in the formation.

.[.The logging means employed to obtain the logging measurements in boththe initial and second log can be any suitable logging means which willdetermine reservoir properties. For example, logging.]. .Iadd.Logging.Iaddend.means capable of producing a resistivity log, a sonic log, or adensity log can readily be employed in carrying out the method of thepresent invention.

After the initial logging data has been obtained the residual oil in thearea of investigation is flushed from the formation by any suitableflooding technique. For example, one can employ any suitable miscibleflooding technique to remove substantially all of the residual oil fromthe reservoir rock around the bore hole in the area of investigation.The term miscible flooding technique is to be understood to includechemical flooding procedures and other well known procedures such assolvent displacement, micellar solution, microemulsion and the like.

When employing a chemical flood, an effective amount of an aqueoussolution containing a surface active agent is injected into theformation being tested. The concentration of surface active agent in theaqueous solution can vary widely but will generally vary within therange of from about 0.5 to 60 weight percent. The particularconcentration employed will also be dependent on the viscosity of theformation oil encountered. Such surface active agents and chemicalflooding techniques are well known in the art. Illustrative of surfaceactive agents which can be employed in chemical flooding processes are:

A. Nonionic

I. Products obtained by autocondensation of various fatty matter andtheir derivatives with ethylene oxide, propylene oxide, glycols, orglycerols:

a. a fatty acid plus ethylene oxide or glycerol, such as palmitic acidplus 5 moles ethylene oxide or glycerol monostearate;

b. an alcohol plus ethylene oxide, such as hydroabietyl alcohol plus 15moles ethylene oxide;

II. Products obtained by condensation of phenolic compounds havinglateral chains with ethylene or propylene oxide. Examples are disecbutylphenol plus 10 moles ethylene oxide and octyl phenol plus 12 molesethylene oxide.

B. Cationic

I. Neutralization product of primary, secondary, or tertiary amine withan acid such as trimethyl octyl ammonium chloride, lauryl dimethylbenzyl ammonium chloride and the like, commonly referred to asquaternary ammonium chlorides.

C. Anionic

I. Alkyl aryl sulfonates such as ammonium isopropyl benzene sulfonate;

II. Fatty alcohol sulfates such as sodium 2-methyl-7-ethyl-4 hendecylsulfate;

III. Sulfated and sulfonated amides and amines such as sodiumN-methyl-N-oleyl taurate;

IV. Sulfated and sulfonated esters and ethers such as dioctyl sodiumsulfo succinate;

V. Alkyl sulfonates such as sodium dodecyl sulfonate.

D. Ampholytic

I. Molecules where the molecule as a whole forms a zwitterion such ascetylaminoacetic acid.

A reference book which describes many types of surfactants suitable asfoaming agents is "Surface Active Agents and Detergents," volumes I andII, by Schwartz et al., Interscience Publishers.

Another method which can be employed for displacing the residual oil inthe formation being investigated is known as miscible flooding and isset forth in U.S. Pat. No. 3,170,513, issued Feb. 23, 1965, and entitled"Method of Miscible Flooding." In this method, a suitable volume of lowmolecular weight hydrocarbons is employed as the displacementhydrocarbon in combination with water. Once the low molecular weighthydrocarbon and water have been injected into the formation, a gas, incombination with water, is injected into the formation to push thedisplacement hydrocarbon through the oil bearing formation, therebydisplacing the residual oil in the formation under investigation.Injection of the displacement hydrocarbon together with water is done insuch volumes that a sufficient amount is placed in the reservoir topermit a miscible displacement of the reservoir oil by the displacementhydrocarbon and miscible displacement thereof by the gas.

The total injected hydrocarbon necesssary to maintain miscibledisplacement within the reservoir should be an amount from about 3 toabout 15 percent, preferably 5 percent, of the hydrocarbon-filled porespace of the reservoir, as readily determinable by means known in theart. The mixture of displacement hydrocarbon and water moves through thereservoir in the same areas without appreciable gravity separation dueto the fact that the injection hydrocarbon moves through the interior ofthe channels between the particles to displace the hydrocarbons, and thewater moves through the remainder of the channels and adjacent theconnate water. Therefore, the injected hydrocarbon provides displacementefficiency, and the water provides volumetric efficiency. Movement of afluid through porous media is related to the saturation or proportion ofthe fluid present due to the inherent effects of the relativepermeabilities of the reservoir. The velocity of movement of water or ahydrocarbon is calculated at any given saturation from the relativepermeability at that saturation, the fluid viscosity, and the saturationchange from the previous condition to the saturation underconsideration. In the mixture of displacement hydrocarbon and waterinjected, the proportion of water is such that the velocity of movementof water is in excess of the velocity of liquid petroleum gas by atleast 5 percent, and preferably in the order of 30 to 50 percent,thereby allowing larger volumes of water to be utilized during theinjection of the hydrocarbon volume required for efficient miscibility.

The miscible displacement technique is also disclosed and set forth inU.S. Pat. No. 3,249,157 issued May 3, 1966 and entitled "RecoveryProcess for Producing Petroleum." Fluids which can be used to misciblydisplace oil from the reservoir under investigation are set forth toinclude, but are not limited to, gaseous and liquified butane andpropane, liquified petroleum gas (L.P.G.), acetone, propyl alcohol,dioxane, carbon tetrachloride and ethane. Non-hydrocarbon fluidsmiscible with, or highly soluble in, the oil at relatively higherpressures can be used and include carbon dioxide, hydrogen sulfide,nitrous oxide, and sulfur dioxide.

Micellar solutions can also be employed in the flooding of the formationto displace the residual oil by a miscible-type mechanism. In employingthis technique, a slug of micellar solution is injected into thereservoir, followed by a bank of thickened water to prevent prematurebreak-through of the final drive water. Generally, a 3 to about 20percent pore volume slug of the micellar solution is employed; and, theamount of thickened water is sufficient to insure that the micellarsolution has been forced completely into the formation being tested.These micellar solutions are surfactant-stabilized dispersions of oiland water, and may contain small quantities of other additives.Generally, the micellar solution contains:

1. Water or a water solution of one or more inorganic solutes thatremain soluble when the solution is contacted by the components of thereservoir formation;

2. At least one surface active material having the properties thatnormally characterize a surfactant and as defined previously; and

3. An amphiphilic coupling agent comprising a polar organic materialhaving a low water solubility.

Suitable aqueous liquids include: water; water solutions of alkali metalhydroxides, such as sodium hydroxide, potassium hydroxide, and the like;water solutions of salts such as sodium carbonate, sodium chloride,sodium bisulfate, and mixtures thereof. The pH of the aqueous liquid ispreferably adjusted to one that is compatible with both an active formof the surfactant and the materials that will be encountered during thepassage of the liquid through the reservoir formation.

Suitable surfactants include: the soaps of fatty acids, such as oleic,linoleic, hydroxy stearic, etc.: the soaps of mixed organic acids, suchas the tall oil fatty acids, tall oil pitch, rosin acids, the petroleumnaphthenic acids, and the soybean oil fatty acids; the surface activeorganic sulfonates and sulfonic acid salts, the nonionic and cationicsurface active materials, and the like, e.g., surface-active materialssuch as those described under the classification of detergent compoundsin Industrial Detergency by William W. Niven, Jr., Reinhold PublishingCo., New York, 1955.

Suitable amphiphilic coupling agents include: the higher molecularweight, monohydroxy aliphatic and alicyclic alcohols, such as thosecontaining six or more carbon atoms; the aromatic hydroxylic compoundssuch as the phenols, and cresols; the pine oils; the sterols;cholesterols; bile salts; fatty acids containing six or more carbonatoms; amines or esters of low water solubility.

In forming the present solubilizing solutions, the selection of theconcentration at which the surfactant is dissolved in the aqueous liquidis preferably based on the critical concentration for micelle formation(abbreviated CMC) for such a system at the temperature of the reservoirformation. The surfactant concentration is preferably at least equal tothe CMC proportions and may exceed them to the extent that iseconomically advantageous. In general, increasing the proportion ofsurfactant increases the oil solubilizing capacity, the viscosity andthe cost of the solubilizing solution. The selection of theconcentration at which the amphiphile is dissolved in the surfactantmicelles is preferably based on the amount required to saturate thesolution at the temperature of the reservoir formation. This can bedetermined by maintaining a portion of the aqueous liquid solution ofthe surfactant micelles at the temperature of the reservoir formationand adding portions of the amphiphile until the addition of anadditional portion causes the solution to remain turbid. The amphiphileconcentration is preferably one lying between the proportion of theamphiphile that is required to saturate the aqueous liquid and theproportion that is required to saturate the micelles.

The bank of thickened water is employed as a mobility buffer to assurestable movement of the slug of micellar solution. The thickening agentcan be any suitable agent such as high molecular weight water-solublepolymers which are well known in the art, e.g. polyacrylamide,sulfonated polystyrene, and the like.

Yet another technique which can be employed to remove substantially allof the residual oil from the formation under investigation is known asthe microemulsion oil recovery process in which microemulsion formingsolutions are employed to drive the oil from the formation. Such aprocess is disclosed in U.S. Pat. No. 3,373,809, issued Mar. 19, 1968and entitled "Microemulsion Oil Recovery Process" and U.S. Pat. No.3,254,714, issued June 7, 1966 and entitled "Use of Microemulsions inMiscible-Type Oil Recovery Procedure," each of which are herebyincorporated by reference.

In this process, a small bank of an oil component, such as petroleumcrude, "light end" kerosene, toluene, or other light aromatic oils,paraffinic oils, and the like, is injected into the formation underinvestigation. Thereafter, an aqueous slug containing suitableconcentrations of polar organic compounds and surfactants is injectedinto the formation. The concentrations of the polar organic compounds inthe aqueous slug can vary widely, as can the concentrations of thesurfactants. Generally, the concentration of the polar organic compoundor compounds will range from about 15 to 60 percent by weight, dependingprimarily upon the selection of the surfactant, and the relative easewith which the reservoir oil or injected oil forms microemulsions. Theconcentration of surfactant (s) will generally range from about 5 to 40percent by weight, based on the total weight of the injected aqueoussolution.

Suitable examples of polar organic compounds for use in accordance withthe invention include the n-, cyclo- and iso-alcohols having 4-16 carbonatoms per molecule; the n-, cyclo- and iso-amines having 5-12 carbonatoms per molecule; phenol and phenols having side chains with 1-10carbon atoms per molecule; n-, cyclo- and isomercaptans having 2-10carbon atoms per molecule; glycols having 2-12 carbon atoms permolecule; fatty acids having 6-22 carbon atoms per molecule; glycerolshaving 3-18 carbon atoms per molecule; ketones having 5-18 carbon atomsper molecule; ethers having 4-18 carbon atoms per molecule; aldehydeshaving 4-18 carbon atoms per molecule; and mixtures of two or more ofthe above. All these molecules may contain saturated or unsaturatedcarbon-carbon bonds.

Suitable surfactants include anionic and nonionic compounds, forexample, sulfonated aromatic hydrocarbons, ethylene oxide condensates ofaliphatic acids, alkyl aryl polyalkylene glycol ethers, esters ofsulfosuccinic acid, mono- and dibasic carboxylic acids, alkyl and arylsulfates; specific examples of which include isopropyl naphthalenesodium sulfonate, sulfonated petroleum distillates, ethylene oxidecondensates of coco fatty acids, octylphenyl polyoxyethylene ether,diisooctyl sodium sulfosuccinate, perfluorocaprylic acid, diisohexylsuccinic acid, dodecyl sulfate and amylphenyl sulfate.

Specific combinations of a polar organic compound and a soap ordetergent for use in the present invention include phenol and sodiumoleate; phenol and sodium abietate; phenol and ethanolamine oleate, pineoil and sodium oleate; glycerol and turkey red oil; diethylene glycoland turkey red oil; octyl alcohol and potassium myristate; octylamineand potassium myristate; octyl mercaptan and potassium myristate; cetylalcohol and oleic acid; p-methyl cyclohexanol and oleic acid; oleic acidand sodium oleate; n-amyl alcohol and an octylphenyl polyoxyethyleneether obtained by reacting 13 mols of ethylene oxide with octyl-phenol(Triton X-102).

Other suitable techniques can be employed to displace the residual oilin the formation. Such other methods include, but are not limited to,alcohol displacement techniques, overbased surfactant water floodingtechniques, and any other suitable flooding techniques or oildisplacement techniques which are well known in the art.

Once the residual oil has been removed from the formation underinvestigation by any suitable flooding treatment such as these describedabove, the formation is then saturated with water, either originalformation water or brine water, so that the formation is substantially a100 percent water bearing reservoir formation. A second log is run onthe water saturated formation to obtain logging data measurements. Thesesecond measurements are then compared with the measurements obtained bythe initial log and the difference represents the amount of residual oilpresent in the formation.

To better illustrate the invention the following Examples are set forth.However, it is to be understood that the examples are for illustrativepurposes only and are not intended to limit the scope of the presentinvention:

EXAMPLE I

In order to determine the residual oil present in a formation which hasbeen penetrated by the borehole of a well the sequential steps are asfollowed:

1. A resistivity log is made on the formation in question. The reservoirrock around the borehole contains, at this point in time formation waterand an undetermined amount of residual oil. The resistivity log providesa measurement designated R₁ (ΩM).

2. an aqueous solution containing a surface active agent (an overbasedsulfonate derived from a petroleum refining steam, e.g. pale oilextract, as set forth in U.S. Pending Patent Application 322,922, ) isinjected into the formation through the borehole of the well. Sufficientsolution is injected to insure that the residual oil has been displacedfrom the vicinity of the borehole to a distance exceeding the radius ofinvestigation of the logging tool.

3. Brine water is then injected into the chemically cleaned formation toresaturate same and thus cause same to be substantially a 100 percentwater-bearing reservoir rock.

4. A second resistivity log is made on the formation. This resistivitylog provides a measurement designated as R₀ since the formation is 100percent water saturated.

In other words, the residual oil saturation (ROS) can readily bedetermined using the following mathematical considerations:

    (R.sub.1) (1-ROS).sup.n = (Rwl) (F)                        Eq. (1)

where

R₁ = log response No. 1

n = saturation exponent

Rwl = formation water resistivity, both during log response No. 1 andNo. 2.

F = formation factor (as related to porosity)

If ROS = O, e.g. water saturation (S_(W)) = 1.0, then

    R.sub.0 = (Rwl) F.                                         Eq. (2)

Therefore, combining Equation (1) and (2) ##EQU1##

    ROS = 1 = (R.sub.0 /R.sub.1).sup.1/n                       Eq. (3)

By employing deep investigating logging devices one can obtainmeasurements farther into the formation, thus providing a morerepresentative value for ROS than has heretofor been possible. Inaddition, it should be noted that method does not require knowledge ofreservoir porosity. Elimination of the porosity parameter and the factthat the three remaining parameters can all be determined with acomparatively high degree of accuracy renders the above described methoda highly reliable one.

EXAMPLE II

In this example the same sequential steps set forth in Example I areemployed with the exception that reservoir rock contains only residualoil (no formation water) and the logging tool employed is an acousticlogging tool which measures the travel time (sec/ft.) of sound throughthe formation over a fixed distance. The tool response can be expressedas follows:

    Δt = 0* Δt.sub.fl + (1 - 0)* Δt.sub.ma   (1)

or expressed in corresponding velocities ##EQU2## where Δt = transittime from log reading

Δt_(fl) = transit time of pore fluid

Δt_(ma) = transit time in rock matrix

0 = porosity of reservoir rock

v_(p) = compressional velocity

v_(fl) = fluid velocity

v_(ma) = rock matrix velocity

Since the residual oil has been removed from the formation being testedafter the initial log was run and before the second log, the differencein the acoustic signal will be a direct function of the amount ofresidual oil. This is true due to the fact that brine and oil havedifferent acoustic properties, such as compressional velocities as shownbelow.

    ______________________________________                                        Liquid            V.sub.p (ft/sec)                                            ______________________________________                                        Petroleum         4200                                                        Water 200,000 ppm NaCl                                                                          5500                                                        100,000 ppm NaCl  5200                                                        0 ppm NaCl        4800                                                        ______________________________________                                    

Therefore, after the reservoir under test has been cleaned of theresidual oil and the formation saturated with brine the difference inthe sonic response in log 1 and log 2 is due to the amount of residualoil present in the formation. Such can be expressed as follows:

    Δ(Δt).sub.log 1,2 =f(Δt.sub.fl).sub.ROS,ROS.sub.=0 =f(ROS)

since the formation contains only residual oil it sometimes isadvantageous to preflush the formation with high salinity brine toenhance the sonic response between oil and the brine. When suchpreflushing step is employed the water injected subsequently to producethe water saturated formation is the same as that employed in thepreflushing step.

EXAMPLE III

In this example, density logs are employed to determine the amount ofresidual oil present in a formation which has been penetrated by theborehole of a well. The method involves the following sequential steps:

1. a density log is made on the formation in question. The reservoirrock around the borehole contains formation water and an undeterminedamount of residual oil.

2. After the density log has been obtained the formation underinvestigation is cleaned of the residual oil by the use of micellarsolutions. Sufficient solution must be injected into the formation toinsure that the residual oil has been displaced from the vicinity of theborehole to a distance exceeding the radius of investigation of thelogging tool.

3. Water, either original formation water, or injection water, is theninjected into the cleaned reservoir rock so that same is substantially100 percent water saturated.

4. A second density log is made on the formation. This log measures thebulk density of the water-saturated rock in the formation.

The oil saturation (So) remaining in the reservoir rock after primaryrecovery can thus be determined using the following mathematicalconsiderations:

General density log response:

φ_(b) = 0φ_(fl) + (1 - 0)φ_(ma)

where

φ_(b) = bulk density measure by log

φfl = density of fluid in pore space of reservoir rock.

φma = matrix density of reservoir rock

0 = porosity of reservoir rock

Based upon the data received from the formation using the abovedescribed log-inject-log technique, one can write the following:

Logging measurements from first density log (Step 1) are represented asfollows:

φb₁ = 0φ_(fl) + (1 - 0)φ_(ma)

where

So ≧ ROS

Logging measurements from second density log (Step 4) are represented asfollows:

φb₁ = 0φ_(fl).sbsb.2 + (1 - 0)φ_(ma)

where

So = 0

φb₂ - φb₁ = Δφ₂,.sbsb.1

where

φb₂ > φb₁

φfl₂ - φf₁ = Δφf₂, 1

where

φfl₂ > φfl₁

Combining the response of the first log and the second log. ##EQU3##Δφf2,1 = f (So) where

So ≧ ROS

Since the properties of the water injected into the formation (Step 3)and the produced hydrocarbon, in addition to reservoir conditions,pressure and temperature are known, the value Δφf₂, 1 represents theamount of residual oil in the formation being tested.

From the above examples and detailed description of the preferredembodiments it can readily be seen that by employing the method of thepresent invention one can readily and accurately determine the amount ofresidual oil remaining in an oil bearing formation after primaryproduction of said formation. In addition, it is evident that certainmodifications can be made in practicing the method of the presentinvention without departing from the scope of same which is defined inthe appended claims.

Having thus described the invention, we claim:
 1. A method fordetermining the residual oil in an oil bearing formation penetrated bythe bore hole of a well comprising the steps of:a. logging saidformation to obtain logging data measurements of the relative quantitiesof residual oil and formation water present in the formation; b.injecting into said formation, through said borehole, a sufficientamount of an oil miscible solution, to displace substantially all of theresidual oil in said formation surrounding said borehole to a distanceexceeding the radius of investigation of the logging means providing thelogging data; c. injecting into said formation through said borehole asufficient amount of water to displace substantially all of said oilmiscible solution and cause said formation being tested to besubstantially 100 percent water saturated; and d. logging for a secondtime said formation to obtain logging data measurements; and, e.comparing the logging data measurements of said second log with thelogging data measurements of said first log to determine the amount ofresidual oil in said formation.Iadd., wherein said logging datameasurements are obtained by employing a reservoir property loggingmeans selected from the group consisting of resistivity log means, soniclog means and density log means.Iaddend.. .[.2. The method of claim 1wherein said logging data measurements are obtained by employing areservoir property logging means selected from the group consisting ofresistivity log means, sonic log means and density log means..].
 3. Themethod of claim 1 wherein said oil miscible solution is an aqueoussolution containing from about 0.5 to 60 weight percent of a surfaceactive agent. . The method of claim 3 wherein said surface active agentis an overbased pale oil extract sulfonate.
 5. The method of claim 1wherein said oil miscible solution is a mixture of liquified lowmolecular weight hydrocarbon and water, said hydrocarbon being presentin an amount of from about 3 to 15 percent of the reservoir hydrocarbonpore space and said water being in an amount such that the movementvelocity of said water in said reservoir is greater than the movementvelocity of said hydrocarbon in said reservoir.
 6. The method of claim 1wherein said oil miscible solution is a micellar solution and from about3 to 20 percent pore volume of said micellar solution is injected intosaid formation.
 7. The method of claim 1 wherein said oil misciblesolution is microemulsion forming solution and said microemulsionforming solution is an aqueous solution containing from about 15 to 60weight percent of a polar organic compound and from about 5 to 40percent by weight, based on the total weight of said aqueous solution,of a surface active agent.
 8. The method of claim 7 which includes thestep of injecting a minor amount of an oil component miscible with thereservoir oil into said formation prior to injection of saidmicroemulsion forming solution.